HCEMATOZOA. 121 



In Europe no entozoon is known which has its 

 normal habitat in the blood-vessels of man ; but in 

 Egypt a trematode worm, discovered in 1851, and 

 belonging to the genus Distomum is frequently found 

 in the abdominal veins. 



It exists in the portal, mesenteric, splenic, intes- 

 tinal, and visceral veins ; it does not appear to pro- 

 duce any serious disorder of the principal trunks of 

 those vessels, but it causes grave compHcations when 

 it is contained in the capillaries of the mucous 

 membrane. 



When this hoematozoon (the distomum hoemato- 

 bium) is situated in the vessels of the waUs of the 

 bladder, it gives rise to marked structural lesions. 

 The mucous membrane is swollen, and is studded 

 with numerous circumscribed spots, considerably 

 injected with blood, which is also extravasated in 

 large quantity, or the membrane is covered with 

 tenacious yellowish masses of exuded mucus, in 

 which the ova of the worms are imbedded. In more 

 advanced stages, the exudations and partial ecchy- 

 moses are increased in size and in number ; and the 

 discoloured elevations, together with the extravasated 

 blood, frequently form a soft coat, which is so firmly 

 connected with the mucous membrane, that when it 

 is detached part of the membrane is removed with 

 it. The ova of the worms sometimes give a sandy 

 appearance to the urine. 



The mucous membrane of the ureter, and in 

 some rare cases that of the pelvis of the kidney also, 

 are affected similarly to the corresponding investment 

 of the bladder ; and the aggregation of the ova, 

 exudation corpuscles, and crystals of uric acid, forms 



